Shoji Mitsuru, Imai Hiroki, Shiina Isamu, Kakeya Hideaki, Osada Hiroyuki, Hayashi Yujiro
Department of Industrial Chemistry, Faculty of Engineering, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan.
J Org Chem. 2004 Mar 5;69(5):1548-56. doi: 10.1021/jo0355303.
An oxidative dimerization reaction, involving the three successive steps of oxidation, 6 pi-electrocyclization, and Diels-Alder reaction, has been experimentally and theoretically investigated for the three 2-alkenyl-3-hydroxymethyl-2-cyclohexen-1-one derivatives epoxyquinol 3, epoxyquinone 6, and cyclohexenone 10. Of the sixteen possible modes of the oxidation/6 pi-electrocylization/Diels-Alder reaction cascade for the epoxyquinone 6, and eight for the cyclohexenone 10, only the endo-anti(epoxide)-anti(Me)-hetero and endo-anti(Me)-hetero modes are, respectively, observed, while both endo-anti(epoxide)-anti(Me)-hetero and exo-anti(epoxide)-anti(Me)-homo reaction modes occur with the epoxyquinol 3. Intermolecular hydrogen-bonding is found to be the key cause of formation of both epoxyquinols A and B with 3, although epoxyquinone 6 and cyclohexenone 10 both gave selectively only the epoxyquinol A-type product. In the dimerization of epoxyquinol 3, two monomer 2H-pyrans 5 interact with each other to afford intermediate complex 28 or 29 stabilized by hydrogen-bonding, from which Diels-Alder reaction proceeds. Theoretical calculations have also revealed the differences in the reaction profiles of epoxyquinone 6 and cyclohexenone 10. Namely, the rate-determining step of the former is the Diels-Alder reaction, while that of the latter is the 6 pi-electrocyclization.
针对三种2-烯基-3-羟甲基-2-环己烯-1-酮衍生物环氧喹诺醇3、环氧醌6和环己烯酮10，对涉及氧化、6π-电环化和狄尔斯-阿尔德反应这三个连续步骤的氧化二聚反应进行了实验和理论研究。对于环氧醌6的氧化/6π-电环化/狄尔斯-阿尔德反应级联的16种可能模式以及环己烯酮10的8种可能模式，分别仅观察到内型-反式（环氧化物）-反式（甲基）-杂环和内型-反式（甲基）-杂环模式，而环氧喹诺醇3则同时出现内型-反式（环氧化物）-反式（甲基）-杂环和外型-反式（环氧化物）-反式（甲基）-同环反应模式。发现分子间氢键是生成环氧喹诺醇A和B与3的关键原因，尽管环氧醌6和环己烯酮10都仅选择性地生成环氧喹诺醇A型产物。在环氧喹诺醇3的二聚反应中，两个单体2H-吡喃5相互作用，形成通过氢键稳定的中间体复合物28或29，然后发生狄尔斯-阿尔德反应。理论计算还揭示了环氧醌6和环己烯酮10反应历程的差异。即，前者的速率决定步骤是狄尔斯-阿尔德反应，而后者的速率决定步骤是6π-电环化。
